This application is based on and claims priority to Japanese Patent Application No. Hei 11-323335, filed Nov. 12, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
This invention generally relates to a control system for an internal combustion engine. More particularly, this invention relates to an apparatus and method for controlling fuel injection amount and idle speed of a marine engine.
2. Description of the Related Art
Outboard motors are powered by engines contained within an engine compartment of the outboard motor. The outboard motors are conventionally attached to watercraft to power the watercraft in a forward or reverse direction. As is known, the engine of a marine craft is subject to increased loading when compared to that of an automobile, for instance. This increased loading generally results from the nature of the marine craft drive system and the environment in which the marine craft is used.
The engines that power the outboard motors may contain an intake system featuring a bypass passage. The bypass passage typically is linked to the intake system upstream and downstream of a throttle control valve. As is known, the throttle control valve controls the amount of air flowing through the induction system into the engine for combustion. When the throttle control valve is closed, the air flow rate is minimized and when the throttle control valve is opened, the flow rate through the induction system can be somewhat controlled. The use of a bypass passage allows air to bypass the throttle control valve for supply to the engine even when the throttle control valve is closed. In some instances, an ISC, or idle speed control valve, is positioned along the bypass passage. The ISC valve can be used to fine tune the idling engine speed when the throttle control valve is in a closed position.
Conventional ISC valves are designed to open when the throttle valve suddenly closes following a period of high speed operation. It is thought that by opening the ISC valves when the throttle valve closes, misfiring and stalling can be obviated or greatly reduced. Generally speaking, the ISC valves are closed when the throttle valve is opened and when the engine speed is low. The ISC valves are then opened when the throttle valve is closed and when the engine speed is high. In some applications, the ISC valves can be suddenly opened during high speed operation of the engine and then gradually closed after the engine speed decreases below a preset level.
The positioning of the idle speed control valve often is controlled by inexpensive step motors. The inexpensive step motors typically have a slow response characteristic. In other words, the command to move is followed by a slight delay before the movement occurs. Because of the resulting slow opening rate of the idle speed control valve, the air flow through the induction system typically does not properly match the desired change of the engine speed resulting from the rapid change in a throttle opening position. Accordingly, the engine can stall or misfire due to an inadequate supply of intake air. One way of correcting this is to provide an idle speed control valve in which the ISC valve opens more rapidly for each input signal to the stepper motor. A drawback from this approach is that a large ISC valve is required and the larger ISC valves increase cost and weight.
Another solution to the misfiring and stalling of the engine is to make the ISC valve more accurately follow the changes in a throttle angle and consequently the engine speed. Preferably, this arrangement would result in the ISC valve being maintained in an open position while the throttle angle is open. This arrangement ensures that a more-than-adequate air supply is provided when the throttle angle is rapidly decreased. The ISC valve then can close with the throttle valve.
In some arrangements, a controller determines the proper amount of fuel to be injected by observing one or more operating condition of the engine. For example, the engine speed and the intake air pressure (indicating the amount of air being introduced by the intake air passage) conventionally are used. Controllers typically are given an optimized fuel injection amount based on each operational engine speed and intake air pressure. Another similar method is to control the fuel injection amount based on engine speed and throttle angle opening. Both of the methods have their own disadvantages.
Fuel injection control based at least in part on intake pressure is particularly problematic during transition from small throttle angle opening to large throttle angle opening. During this transition, the amount of air being introduced into the combustion chamber is difficult to measure. This is because typical intake pressure sensors observe pressure wave troughs to determine pressure in the intake air passage. As throttle opening increases, the pressure oscillation frequency increases until adjacent pressure waves are superimposed and begin to cancel. Therefore, the controllers receive inaccurate air pressure information and output non-optimal fuel injection amounts.
Fuel injection amounts based on throttle opening are also non-optimal because, in the transitional region, the air contribution through the bypass passage is not always properly accounted for. For instance, although the ISC valve is open it may not be fixed in an open position. This can result in unpredictable introduction of air through the bypass passage. This problem becomes even more pronounced when the engine speed is low (throttle valve closing). In that state, the amount of air introduced through the bypass passage as a percentage of total air introduced into the combustion chamber is relatively large.
Accordingly, an arrangement is desired in which the ISC valve is substantially fixed when the throttle valve has an angle above a preset value. An arrangement is also desired in which the fuel injection amount is accurately determined based on intake air pressure, engine speed and throttle angle position, depending on operational ranges of the engine. For instance, a control strategy referencing intake pressure and engine speed can be used below a preset throttle opening while a control strategy referencing throttle valve position and engine speed can be used above the preset throttle angle.
Thus, one aspect of the present invention involves providing a control system whereby the position of the ISC valve is substantially fixed above a preset value and the fuel injection amount inputted to the fuel injectors is a function of the air intake pressure, the engine speed and the throttle valve opening.
A further aspect of the present invention involves a marine engine for a watercraft comprises a cylinder block. At least one bore is formed in the cylinder body. A piston is mounted for reciprocation within the cylinder bore. A cylinder head assembly is disposed over a first end of the cylinder bore forming a combustion chamber with the piston and cylinder bore. A journaled crankshaft is drivingly connected to the piston by a connecting rod. An intake air passage is in fluid communication with the combustion chamber at one end and in fluid communication with a plenum chamber at the other. An intake valve positioned between the intake air passage and the combustion chamber allows for timed introduction of the air/fuel mixture. A throttle valve is pivotally mounted in the air intake passage for defining the amount of air flowing in the air intake passage. A fuel injector for forming the air/fuel mixture is connected to the air intake passage at a point downstream from the throttle valve. A bypass passage is in fluid communication with the plenum chamber and the air intake passage downstream from the throttle valves. An ISC valve pivotally mounted in the bypass passage is driven by an actuator for determining the amount of air flowing in the bypass passage. An angle position sensor juxtaposed with the crankshaft signals engine speed to an ECU. A intake pressure sensor signals intake air pressure downstream of the throttle valve to the ECU. A throttle valve position sensor connected to the throttle valve sends signals throttle valve opening to ECU. The ECU, using at least two signal inputs determines fuel injection amount and signals that fuel injection amount to the fuel injector(s). The ECU, using at least one signal input, determines the correct position for the ISC valve, and communicates that value to an actuator. The actuator drives the ICS valve to the correct position.
Another aspect of the present invention involves a method of operating a internal combustion marine engine. The method comprises the steps of (a) sensing at least one running condition of the engine, (b) comparing the at least one running condition to a preset value, (c) determining a target ISC valve opening if the at least one running condition is greater than the preset value, (d) sensing the current ISC valve opening, comparing the target ISC valve opening with the current ISC value, (e) driving the ISC valve with the stepper motor if the sensed ISC valve opening is not about equal to the target ISC valve opening, and (f) continuing the steps (a)-(e) while the engine is running.
A further aspect of the present invention involves a method of controlling an idle speed control valve in a marine engine for a watercraft. The method involves sensing throttle position and moving the ISC valve if the throttle position is less than a first preset value. If the throttle position is greater than the first preset value, the method involves substantially fixing the ISC valve at a fully open position. The method also involves sensing engine speed, intake pressure and throttle angle opening. Below the first preset throttle angle, the method involves determining the fuel injection amount based on engine speed and intake air pressure. Above a second preset throttle angle, the method involves determining the fuel injection amount based on the engine speed and the throttle position. Between the first and the second preset throttle angles, the method involves determining the fuel injection amount based on both the engine speed, the intake air pressure and the throttle angle.